Semiconductor transistors, in particular field-effect controlled switching devices such as a Metal Oxide Semiconductor Field Effect Transistor (MOSFET) or an Insulated Gate Bipolar Transistor (IGBT) have been used for various applications including but not limited to use as power switches in power supplies and power converters, electric cars, air-conditioners, and even stereo systems. For example, power MOSFETS are used as low-side and high-side power switches in bridge circuits to drive an electric motor. Typically, the switching states of the power switches are monitored in such a bridge circuit to properly synchronize them. This is to avoid, for example, that the low-side switch is switched on prior to switching off the high-side switch. This typically requires that the driver of the low-side switch is connected to the high-side switch to evaluate the switching state of the high-side switch. Likewise, the driver of the high-side switch is typically connected to the low-side switch to evaluate the switching state of the low-side switch in the bridge circuit.
Due to the different voltage levels of the low-side switch and the high-side switch, two level-shifter are typically used in bridge circuits, for example a step-up level-shifter between the low-side switch and the driver of the high-side switch and a step-down level-shifter between the high-side switch and the driver of the low-side switch. Accordingly, the voltage difference between the low-side arm and the high-side arm of the bridge circuit is mainly taken by the level-shifter so that a rated breakdown voltage of the driver circuitry for the high-side switch and the low-side switch, respectively, may only be given by the gate voltage, which may be about 1 V to about 20 V for n-channel MOSFETs. Typically, the level-shifters are integrated into respective driver-ICs (integrated circuits), for example a common MOSFET driver stage circuit. For power applications, in particular for voltages of about 400 V or even more than about 600 V, the driver ICs of the bridge circuits are however expensive due the required high voltage blocking capability.
Accordingly, there is a need to improve bridge circuits for power applications.